The present invention relates to a process whereby cis isomers of certain preferred cyclopropanecarboxylic acids may be isolated from an isomeric mixture of cis/trans-cyclopropanecarboxylates. More specifically, it relates to the isolation of a product significantly enriched in cis-3-(2-halo-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxyl ic acid starting with esters of a mixture of cis/trans-3-(2,2-dihalo-3,3,3-trifluoropropyl)-2,2-dimethylcyclopropanecar boxylic acid.
Pyrethroid compounds are known to be useful as insecticides. Amongst these, pyrethroid esters of cis-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarbox ylic acid are more active insecticides than the corresponding esters of the trans isomer of this acid.
However, as demonstrated by U.S. copending application Ser. No. 323,652 (above), which is also directed to the dehydrohalogenation of esters of cis/trans-3(2,2-dihalo-3,3,3-trifluoropropyl)-2,2-dimethylcyclopropanecarb oxylic acid to the corresponding 2-halo-1propenyl compound, the ratio of cis:trans isomers does not vary during the course of this dehydrohalogenation reaction.
These products, and particularly the aforesaid cis isomers, are useful, for example, as foliar and soil insecticides against such insects as species of Diabrotica. Therefore, processes which provide predominant amounts of the cis isomer are especially desired.